Osmotic devices for delivering beneficial agents to environments of use are known to the prior art in U.S. Pat. No. 3,845,770 issued to Felix Theeuwes and Takeru Higuchi, and in U.S. Pat. No. 3,916,899, issued to the same patentees. The osmotic devices disclosed in those patents comprise a semipermeable wall that surrounds a compartment containing an agent. The wall is permeable to the passage of an external fluid, and substantially impermeable to the passage of agent. There is a passageway through the wall for delivering the agent from the device. These devices release agent by fluid being imbibed through the wall into the compartment at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall to produce an aqueous solution containing agent that is dispensed through the passageway from the device. These devices are extraordinarly effective for delivering an agent that is soluble in the fluid and exhibits an osmotic pressure gradient across the wall against the fluid, and for deliverying an agent that has limited solubility in the fluid and is admixed with an osmotically effective compound that is soluble in the fluid and exhibits an osmotic pressure gradient across the wall against the fluid.
A pioneer advancement in osmotic delivery devices was presented to the art by inventor Felix Theeuwes in U.S. Pat. No. 4,111,202. In this patent, the delivery kinetics of the device is enhanced, for delivering agents with degrees of solubility in aqueous fluids that are difficult to deliver, such as very soluble or insoluble in the fluid, by manufacturing the device with an agent compartment and an osmagent compartment separated by a film, which film is movable from a rested to an expanded state. The device delivers agent by fluid being imbibed through the wall into the osmagent compartment producing a solution that causes the compartment to increase in volume and act as a driving force that is applied against the film. This force urges the film to expand against the agent compartment and correspondingly diminish the volume of this compartment, whereby agent is dispensed through the passageway from the device. While this device operates successfully for its intended use, and while it can deliver numerous difficult to deliver agents, its use can be limited because of the manufacturing steps needed for fabricating and placing the movable film in the device. It will be appreciated by those versed in the art, that if a device can be provided without the movable film, and have a compartment containing an agent and an expandable driving member, such as a layer of a swellable hydrogel, that can generate a force for delivering the agent, and can be manufactured free of the tribulations known to the art, such a device would have a positive value and represent an advancement in the delivery arts.